|Publication number||US7317933 B2|
|Application number||US 10/878,501|
|Publication date||Jan 8, 2008|
|Filing date||Jun 28, 2004|
|Priority date||Jul 4, 2003|
|Also published as||US20050014516|
|Publication number||10878501, 878501, US 7317933 B2, US 7317933B2, US-B2-7317933, US7317933 B2, US7317933B2|
|Inventors||Nidham Ben Rached, Thierry Lucidarme|
|Original Assignee||Nortel Networks Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Non-Patent Citations (4), Referenced by (8), Classifications (19), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to the field of radiocommunication with mobile stations. It is applied in particular in mobile station locating systems.
The mobile station locating function of a radiocommunication system consists in estimating the geographical position of a given mobile station, in particular on the basis of the signals which it exchanges over the air interface with a radiocommunication infrastructure. This function has undergone recent developments to take account of the need to locate with accuracy a mobile station whose user is making an emergency call. Thus, there are different locating strategies, some of which (the “cell ID” method, OTDOA (“Observed Time Difference Of Arrival”), location method using the GPS system (“Global Positioning System”)) are described in particular in the technical specification 3G TS 25.305, “Stage 2 functional specification of UE positioning in UTRAN”, version 3.8.0 published in March 2002 by the 3GPP (“3rd Generation Partnership Project”), and in the reference work “Principes de radiocommunication de troisième génération” [“Third-generation radiocommunication principles”] by M. Lucidarme, ed. Vuibert, 2002.
The GERAN network shown in
A general description of the radio interface, referred to as Um, between the mobile stations (MS) 23 and the base stations (BTS) 22 of the BSS is provided in technical specification ETSI TS 101 350, “Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Overall description of the GPRS radio interface; Stage 2 (GSM 03.64, version 8.5.0, Release 1999), published by ETSI (European Telecommunications Standards Institute) in August 2000.
Each base station 22 is supervised by a base station controller (BSC) 21 via an interface known as Abis.
Different location methods are standardized for the GERAN network: the Timing Advance method, the E-OTD (“Enhanced Observed Time Difference”) positioning mechanism, the location method using the GPS system, and the U-TDOA (“Uplink Time Difference of Arrival”) method.
The aforementioned different location strategies do not offer the same performance, and meet different needs. The timing advance or cell ID methods are based on the determination of the serving base station of a given mobile station whose geographical coverage provides a first approximation of the station location. This method, which is advantageous by virtue of its simplicity, obviously lacks precision for certain applications. The GPS method can only be used with mobile stations which are equipped with receivers capable of receiving GPS signals. Its practical implementation further requires the supply of specific data, known as GPS assistance data, by the network infrastructure to the mobile station, in order to improve significantly the performance of the GPRS receiver installed in the mobile station.
The TOA (“Time of Arrival”) or TDOA (“Time Difference of Arrival”) location methods entail a measurement of the arrival time of the received signals. The presence of multipath propagation limits the accuracy with which the time of arrival of the first received signal component can be estimated. This has a significant impact on the performance of the entities responsible for calculating the location of the mobile stations in the network, and imposes a compromise between service accuracy and processing time.
The known methods for estimating the time of arrival of signals are based on the training sequence conventionally comprising bits known a priori to the receiver.
An object of the present invention is to propose methods for estimating the time of arrival of signals which offer improved performance while being particularly suitable for implementation in the context of the location of the mobile stations of a radiocommunication network.
The invention thus proposes a method for measuring the time of arrival at a radiocommunication receiver of a received radio signal, wherein a component of the radio signal received by said receiver and carrying information bits is stored in a memory of a radiocommunication receiver, and an estimation of said information bits is obtained. The obtaining of said estimation comprises demodulating said signal component in the receiver. The time of arrival of the signal is estimated in the receiver on the basis of the estimated bits and the received signal component.
The method according to the invention uses not only pilot bits of a training sequence, but also samples of a received signal component, including bits not known in advance and estimated by the receiver. The algorithm for estimating the time of arrival of the received signal may also work with a received signal component which is significantly larger than a training sequence, enabling optimisation of the performance achieved in terms of processing time and accuracy of results. The samples do not need to be transmitted to a location centre which is separate from the receiver. Their processing is essentially local.
Another aspect of the present invention relates to a method for locating a radiocommunication mobile station wherein measurements of the times of arrival at radiocommunication receivers of radio signals transmitted by the mobile station are carried out using a method of the type outlined above, and the measured times of arrival are processed in order to estimate a location of the mobile station.
Another aspect of the present invention relates to a radiocommunication receiver comprising: a memory to store a radio signal component originating from a transmitting station and carrying information bits; means for obtaining an estimation of said information bits, including a demodulator to which said signal component is applied; and means for estimating the time of arrival of the signal on the basis of the estimated bits and the received signal component.
The invention further proposes a system for locating a radiocommunication mobile station, comprising receivers of the type defined above and means for processing the estimated times of arrival in said receivers in order to estimate a location of the mobile station.
In the present description, the invention will be described more specifically in its non-limiting application to the architecture of the location function according to the U-TDOA method in a GERAN-type network.
The U-TDOA method is based on measurements by the GERAN network of the time of arrival (TOA) of a known signal transmitted by a mobile station and received by a plurality of LMUs. This method requires a sufficient and rational deployment of LMUs in order to guarantee the presence of LMUs in relative proximity to the mobile stations which can be located in order to measure with accuracy the time of arrival of the signals. Since the geographical coordinates of the LMUs deployed are known to the network, the position of the mobile station can be calculated using a hyperbolic trilateration method.
GERAN networks use two types of modulation:
In some control channels and traffic channels of the GERAN networks, the radio signal is transmitted in the form of successive bursts produced by modulating respective blocks, each composed of 26 bits known a priori, which form a training sequence TS, 116 information bits, including 2 signalling bits SB (pre-emption flags) and two times 3 tail bits.
The type of physical channel from which a burst originates is defined on the basis (i) of signalling exchanged in advance between the transmitter and the receiver in order to define the resource type, (ii) the type of modulation used (GMSK or 8-PSK), and (iii) patterns of signalling bits SB inserted in the transmitted frames.
An LMU (25 a, 25 b) carries out measurements of the time of arrival of signals transmitted by the mobile station 23, and transmits these measurements to the SMLC which calculates the geographical position of the transmitting station. The other functions of the LMU are described in paragraph 5.5.4 of the aforementioned specification 3GPP TS 43.059, incorporated into the present text by reference.
The samples of a signal component of each received burst are further stored by the controller 36 in a memory 37 in order to be transmitted subsequently to the module 38 which estimates the time of arrival of the burst. This storage operation is preferably carried out in a time-stamped manner, in the sense that it stores, along with the samples, a date indication taken relative to a time reference within the system. The signal component samples are thus transmitted to the channel sounding module 34 and to the demodulation module 35 which produces the corresponding bit estimations.
When the bits ŝ(t) carried by the decoded received signal component are available at the output of the demodulator 35, the controller 36 transmits them together with the corresponding samples and their time stamp, and also, where applicable, the estimated impulse response ĥ(t), to a module 38 which estimates the time of arrival of the received signal, which measures the time of arrival on the basis of the decoded bits, the corresponding samples and their time stamp. According to the invention, the signal component is not limited to samples corresponding to pilot bits, which are bits known a priori to the receiver 33. The module which estimates the time of arrival of the burst may thus process up to 148 information bits (and not simply the 26 pilot bits), thereby producing a significant processing gain.
The measurement of the time of arrival of the received signal is performed by the estimation module 38 using known methods.
The fact that the method for estimating the time of arrival, and more specifically the calculation of the cross-correlation in the preceding example, are applied according to the invention to signal portions which are longer than the training sequence alone (and can, for example, as indicated below, be applied to the 148 bits of a GSM “burst”, compared with the 26 bits of the training sequence), yields improved accuracy due to the fact that the maximum cross-correlation function occurs in the form of a more pointed peak, which is therefore easier to locate in time. This maximum corresponds to a time shift δ, the accuracy of which depends on the calculation granularity of the discrete cross-correlation function over the observed interval concerned, and which corrects the initial time stamp T.
The invention applies equally to other radiocommunication systems, such as CDMA (“Code Division Multiple Access”) systems. In a spread-spectrum CDMA system, the transmitted bits, which are generally binary (±1) or quaternary (±1±j), are multiplied by spreading codes composed of samples, referred to as “chips”, the rate of which is higher than the bit rate. Orthogonal or quasi-orthogonal spreading codes are allocated to different logical channels sharing the same carrier frequency in order to enable each receiver to detect the sequence of bits intended for it by multiplying the received signal by the corresponding spreading code.
The antenna (31) of an LMU will then, for example, be connected in receive mode via a radio stage 32 to a conventional receiver which carries out coherent demodulation based on an approximation of the impulse response of the radio propagation channel. To estimate an impulse response, the channel sounding module 34 comprises, in a conventional manner, a filter matched to the channel spreading code or to the transmitted sequence of pilot bits concerned. During the reception of a pilot bit, known a priori to the receiver 33, the output of the matched filter is multiplied by the conjugated complex of this pilot bit, which produces an observation of the impulse response. The estimation is obtained by averaging these observations over several tens of pilot bits.
On the basis of this estimated impulse response, the demodulation module 35 carries out coherent demodulation and decoding of a signal component received on the antenna 31. The demodulation may, for example, be carried out by means of a Rake-type receiver. The resulting estimations of the transmitted bits may then possibly be combined in order to obtain a diversity gain. As described above, the resulting estimation of the bits carried by the received signal component is then transmitted with the samples corresponding to a module 38 which estimates the time of arrival of the signal.
In a second embodiment of the invention, in which a plurality of LMUs receive different versions of the same signal transmitted by a mobile station, the receive diversity gain is used to further improve the time of arrival estimation. This example is shown in
Alternatively, if the first estimations are softbits, each LMU 25 a, 25 b, 25 c transmits its first estimation at the request of the SMLC 26. In this example, a particularly reliable estimation produced by an LMU 25 a may be judged sufficiently accurate, given the softbits, to dispense with the combination with other estimations produced by the other LMUs 25 b, 25 c. The SMLC 26 will then no longer require these other estimations, and in return will transmit the estimation judged to be sufficient instead of an estimation produced by the combination. This last method will prevent any overloading of the interface between the SMLC 26 and the LMUs 25 a, 25 b, 25 c.
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|1||Technical Specification 3G TS 25.305, <<Stage 2 functional specification of UE positioning in UTRAN>>, Version 3.8.0 published in Mar. 2002 by the 3GPP.|
|2||Technical Specification 3GPP TS 43.051, <<GSM/EDGE Radio Access Network (GERAN), Overall Description-Stage 2 (Release 4) >>, Version 4.0.0, published in Nov. 2000 by the 3GPP.|
|3||Technical Specification 3GPP TS 43.059, <<Technical Specification Group GSM/EDGE Radio Access Network ; Functional stage 2 description of Location Services (LCS) in GERAN (Release 6)>>, Version 6.0.0, published by the 3GPP, Apr. 2003.|
|4||Technical Specification ETSI TS 101 350, <<Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Overall description of the GPRS radio interface; Stage 2 (GSM 03.64, Version 8.5.0, Release 1999), published by ETSI (European Telecommunications Standards Institute) in Aug. 2000.|
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|US9295021||May 25, 2009||Mar 22, 2016||Commonwealth Scientific And Industrial Research Organisation||Measurement of time of arrival|
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|U.S. Classification||455/556.1, 370/391, 375/149, 455/560, 455/561, 342/357.63, 342/357.25, 342/357.65|
|International Classification||H04Q7/38, H04Q7/20, H04M1/00, G01S3/46, H04Q7/32, G01S19/26, G01S5/02, G01S19/42, G01S19/24|
|Aug 31, 2004||AS||Assignment|
Owner name: NORTEL NETWORKS LIMITED, CANADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BEN RACHED, NIDHAM;LUCIDARME, THIERRY;REEL/FRAME:015057/0271;SIGNING DATES FROM 20040630 TO 20040705
|May 6, 2008||CC||Certificate of correction|
|Jun 22, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Oct 28, 2011||AS||Assignment|
Owner name: ROCKSTAR BIDCO, LP, NEW YORK
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Owner name: APPLE INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ROCKSTAR BIDCO, LP;REEL/FRAME:028676/0856
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